How to Picture a Black Hole

This month, researchers are inaugurating the Event Horizon Telescope, a project that will try to take the first detailed pictures of the supermassive black hole at the center of our galaxy.

This observation would be a remarkable achievement, underscoring the progress that has been made in black-hole research in just the last few decades. As recently as the 1970s, astronomers still argued over whether black holes were theoretical constructs or real physical objects. They now have ample evidence that black holes are not only real, but abundant in the cosmos.

Here on Earth, advanced computer simulations have given astronomers a wealth of information, leading theoretical physicist Kip Thorne of Caltech to suggest that black-hole research is entering a new golden age.

“There is now a program of observations that I expect will bring us some big surprises and hopefully validate the predictions from these simulations,” he said.

Yet it’s still strange to imagine what the area around a black hole looks like. After all, a black hole is an object from which nothing, including light, can escape. In this gallery, we look at some of the predictions that researchers have made about viewing a black hole.

Above:

Black Hole Dead Ahead

If you could get up close and personal with a black hole, there might not be much to see. You couldn't observe the black hole itself, and instead would only glimpse its event horizon — a spherical boundary inside of which nothing can escape.

The black hole itself would sit at the event horizon's center as a point of infinite density known as a singularity. The great amount of mass at this point would stretch the fabric of space-time, bending light coming from behind and creating a gravitational lens.

If you were at a distance of about 375 miles, a black hole 10 times the mass of the sun might appear like the above image. Light from the background Milky Way galaxy is highly distorted, revealing the location of the black hole.

Central Black Hole

Researchers have long studied the enormous black hole at the center of our galaxy, whose mass is more than 2 million times our sun. As seen in the above simulation, an unlucky cloud of gas and dust could get caught up in the black hole’s relentless gravitational pull. Spiraling inward, this mass would be torn apart, with some parts flung off and others slowly consumed.

Despite their fearsome reputation, black holes are not cosmic vacuum cleaners that draw everything into their hungry maw. Objects can form stable orbits around them without getting sucked in. As seen in the simulation, stars near the black hole are tugged around like planets orbiting a star but don’t necessarily fall inward.

The Accretion Disk

Material that falls into a black hole usually doesn’t go directly in. Instead, gas and dust form an accretion disk that spirals around the black hole like water circling a drain.

These accretion disks have unexpected properties. Though astronomers have yet to fully understand the process, the gas and dust generate strong magnetic fields as they fall in and emit copious amounts of energy. This energy is shot out as two jets of material, often traveling a significant fraction of the speed of light.

The above schematic depicts what these jets might look like up close, though astronomers have also captured the powerful emissions in images, such as the one below of galaxy M87 taken by the Hubble space telescope. Occasionally, these jets will turn off for a short time, building up energy and eventually shooting off massive “bullets” of material.

Space-Time Gordian Knot

In the last year, powerful computer simulations have brought the area around a black hole into focus. Theoretical physicist Kip Thorne and his colleagues have modeled the complex equations of general relatively around a black hole and uncovered a host of previously unknown ways that they can bend and warp space-time.

For instance, a spinning black hole produces ripples in the fabric of space-time known as vortexes, depicted as an intricate tangle of lines emerging from the black hole. The consequences are highly chaotic, creating the whirlwind-like behavior seen in the above visualization.

Vortex lines have an odd effect on space-time. If you oriented your body along a vortex line, your head would start to turn relative to your feet, wringing you like a towel. Blue lines in the above video correspond to a clockwise twist while red lines denote counterclockwise movement.

That's Got to Hurt

Let’s say you wanted to see a black hole up close but then you got too near and fell in. That sucks. Just what will happen to your body as you dive into the abyss?

Until recently, all that researchers knew was that the difference in gravity between your head and your feet would stretch you out like a noodle.

New simulations from theoretical physicist Kip Thorne and his colleagues show the actual experience would be even more agonizing and bizarre. Around a black hole, the formulas that govern space-time break up into two separate components.

One part, the vortex lines, twists space-time clockwise or counterclockwise, putting your body through the wringer. The other components, known as tendex lines, stretch and squeeze the curvature of space-time. An astronaut falling toward the equator of a black hole would get pulled apart like taffy while one going to the polar region would get flattened like a pancake.

These effects were so new that Thorne’s team had to come up with a new term to describe them. While vortex -- coming from the Latin word vortere, ‘to turn,’ -- already exists, Thorne’s graduate student, David Nichols, coined the word tendex, which comes from the Latin tendere, ‘to stretch.’

Double Black Hole

The behavior of space-time around a black hole becomes extremely complex when considering two merging black holes. Researchers think this type of event is common, occurring when two black holes form near one another or during the collision of two supermassive black holes at the center of two merging galaxies.

This visualization shows two black holes against a simulated dark blue sky background. Below them is a two-dimensional depiction of the fabric of space-time around the black holes.

The black holes spiral around each other, speeding up as they merge, and eventually coming together to form a single black hole. Space-time wobbles during this merger, throwing off waves of gravitational energy that researchers hope to one day detect from Earth.

Video: The Caltech/Cornell SXS Collaboration

Gravitational Waves

Black hole mergers are expected to be some of the most energetic events in the universe. These powerful collisions should produce ripples in the fabric of space-time, which would travel outward at the speed of light. The above simulation shows how astronomers think these outward traveling waves would appear in the fabric of space-time.

Video: The Caltech/Cornell SXS Collaboration

A New Window

In the next few years, astronomers hope to detect the effects of merging black holes. The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a group of facilities working together to spot these gravitational waves as they pass through the Earth.

If a gravitational wave passed through the Earth, LIGO’s high-precision laser beams would flicker ever so slightly. The collaboration employs two detectors, one in Louisiana and the other in Washington. By determining the difference in detection time between each facility, researchers should be able to pinpoint the strength and location of a source.

The LIGO team is currently working to increase their detectors' sensitivity, an upgrade they expect to have done by 2014. The experiments are also working to account for a great deal of background noise. Something as simple as a truck passing outside the observatory could shake the lasers and be mistaken for a signal.

That’s why many scientists hope to someday see a space-based gravitational wave observatory. The European Space Agency is currently looking to fly the Laser Interferometer Space Antenna (LISA), a set of three satellites that would detect gravity waves, giving astronomers a new window on the universe.

NASA was initially going to be a partner on LISA though the agency pulled out in 2011 due to budget cuts.